Study On The DeNo_x Mechanism And Alkali Resistance Of HZSM-5 Modified Cerium Iron-based Catalyst

The development of industry is similar to the construction of a metropolis;the transformation of the process requires considerable human and material resources.There are two sides to everything,and while times are progressing,the human living environment is at great risk.Air pollution is currently the most serious of the environmental pollution problems.Nitrogen oxides（NOx）from the combustion of fossil fuels such as those containing nitrogen is a precursor to acid rain,photochemical smog,ozone layer depletion and the formation of fine particulate matter,and these fossil fuels cannot be completely replaced by new clean energy sources in the short term.With air pollutant emission standards becoming increasingly stringent worldwide,the issue of how to control NOx emissions has become particularly important.Selective catalytic reduction of NOx with NH3（NH3-SCR）has gradually developed into a mainstream de NOx technology applied and promoted by the relevant industries,and zeolite molecular sieve catalysts represented by Cu-SSZ-13 and Cu-SAPO-34 have been industrially applied,but the problems of narrow temperature window for zeolite molecular sieve activity and susceptibility to deactivation by alkali metal（Na,K,etc.）poisoning need to be solved.Therefore,in this paper,some metal oxide-based molecular sieve de NOx catalysts with high activity and strong alkali resistance under different working conditions were developed by an easy industrial physical grinding and impregnation method using cerium iron oxide as the active component and the acidity and special pore structure of HZSM-5 molecular sieve.By combining physical characterization analysis with various in situ characterization analysis tools,the mechanism of HZSM-5 in the SCR reaction process and the anti-poisoning mechanism were investigated in detail from the perspective of catalyst structure and activity correlation.The main studies are as follows:（1）The effect of introducing different levels（5 wt.%～30 wt.%）of HZSM-5 on the catalytic activity of cerium-based catalysts was analysed in detail using a physical grinding method,using pure CeO2 samples without the introduction of HZSM-5 carriers as a comparison.It was found that through a simple process of mechanically adequate mixing of HZSM-5 molecular sieve and cerium nitrate hexahydrate,the catalyst structure orderliness was disrupted and the lattice defects on the cerium dioxide surface increased,which favoured the formation of oxygen vacancies and thus improved the catalytic activity.In addition,the introduction of HZSM-5 acted as a solid acidic additive,thus compensating for the lack of acidity of cerium oxide and facilitating the adsorption of NH3.The introduction of HZSM-5 also weakened the adsorption of NOx,allowing the NH3-SCR reaction to take place over the catalyst,mainly through the Eley-Rideal（E-R）mechanism.（2）The effect of alkali metal Na⁺on the catalytic activity of HZSM-5 molecular sieves modified with magnetic hematite（γ-Fe₂O₃）was investigated,and the mechanism of HZSM-5resistance to alkali poisoning was further investigated with reference to iron-based samples of anatase Ti O₂ crystalline phase carriers.It was found that the loading of the active componentγ-Fe2O3 onto the HZSM-5 molecular sieve by a simple impregnation method yielded a high specific surface area as well as a highly dispersed state of the active component on the surface of the catalyst.The ability of Na⁺to exchange spontaneously into the pore channels of the molecular sieve,hindering Na⁺from poisoning the active components and leaving the reduction of the system unaffected,while reducing the adsorption of Na on NOx,which is the main reason for its high alkali resistance.In addition,the increased number of acidic sites on the surface reduces the negative effects of the acidity of the Na⁺neutralization catalyst surface,leaving the NH3 adsorption capacity unaffected and thus maintaining high SCR activity.The chemisorbed oxygen promotes NO adsorption and oxidation of NO to NO2,resulting in a"fast SCR"reaction.（3）In terms of catalyst design,following the advantages of cheap and easy availability of raw materials,environmental friendliness,and high de NOx efficiency,HZSM-5 improves the thermal stability of the system and is suitable for industrial mass production.It can be widely used in non-electric industries such as steel plants for tail gas de NOx suitable for sintered flue gas emission characteristics.